It really depends what they are. The USA generally have a single rocket per payload, especially the new NROL and GPS space craft as these are big and heavy. SpaceX changed that with the second of their test rockets when the Dragon capsule was released the second stage re-fired and then deployed a second spacecraft.
With some of the Minotaur launches from Wallops Island they have up to 6 different spacecraft. It really depends on the size of the spacecraft, and the lifting power of the launch vehicle. The GPS IIF satellites are now launched on Delta IV ELVs because they are too heavy for the Delta II rockets.